1. Field of the Invention
Embodiments of the invention are generally directed to the field of colored coatings and, more particularly, to an environmentally benign, readily removable, colored coating composition, a method for its application to and removal from a surface, and applications thereof.
2. Related Art Discussion
Sodium alginate is an anionic linear polysaccharide composed of (1-4)-linked D-mannuronic and L-glucuronic acid repeat units as depicted in FIG. 1. These sugar residues can either be arranged in blocks or they can be randomly distributed. Substances containing divalent cations (e.g., calcium, magnesium, others known in the art) can chelate carboxylate groups and make crosslinks between chains, forming an insoluble, non-thermo-reversible hydrogel, e.g., calcium alginate.
Calcium alginate can be used, for example, to make microcapsules for drug delivery and immobilization of biocatalysts, coatings for medical implants, food thickeners and coatings, textile print thickeners, and for other applications where its unique barrier, ion chelating, and biocompatible properties may be useful.
Calcium alginate is a firm, clear, and quick-setting gel that is generally physically stable and flexible when dried. Calcium alginate can be synthesized by combining aqueous sodium alginate and calcium chloride (or other divalent ion) solutions; e.g., calcium complexes such as calcium carbonate and calcium chlorate. Other elements containing divalent cations may include, without limitation, magnesium, manganese, iron, zinc, mercury or non-metal ions such as paraquat; and their combination with sodium alginate may produce hydrolgel compositions suitable as a removable coating, however, not necessarily non-toxic or environmentally friendly. The stability of calcium alginate hydrogel depends on the stability of calcium complexes within the gel. Thus chelating agents that strongly bind calcium (or other elements containing divalent cations) may quickly solubilize the hydrogel. Exemplary compounds that are capable of such quick calcium (and related substance) removal may include, but are not limited to, sodium citrate, disodium ethylenediamine tetraacetate (EDTA), ethylene glycol tetraacetic acid (EGTA), polyanions such as polyvinylacetate, and high concentrations of ionic solutions such as, e.g., sodium thioglycolate and others known in the art.
U.S. Pat. No. 6,653,265 discloses, among other things, a removable marking system. The system comprises a removable paint formulation comprising zinc oxide, water and an adjuvant, and an aqueous removal formulation having a pH of about 4 to 8, comprising an acid and a buffering agent. The background subject matter disclosed in the '265 patent is incorporated by reference herein in its entirety to the fullest allowable extent.
The inventors appreciate that there may be benefits and advantages associated with removable (or, alternatively, reversible) colored coatings, especially those that are non-toxic, biodegradable and environmental benign. More particularly, there are benefits and advantages associated with such colored coatings that can be applied and removed (reversed) essentially on-demand. Non limiting examples of applications of such coatings may include temporary field lines and logos for sports complexes and roadway markings, as well as coatings for plants, fruit, and skin surfaces.